(1) Field of the Invention
The present invention relates to a method and apparatus for detecting combustion variations in an internal combustion engine.
(2) Description of the Related Art
As measures taken against exhaust gas pollution and fuel consumption, various systems for controlling the air-fuel ratio and ignition timing of the engine have been developed. In one of such systems, the air-fuel ratio (or the ignition timing) is controlled by detecting combustion (output) variations.
According to the prior art combustion variation detecting method, a time period T.sub.i required for one revolution of the engine is measured, and a mean engine rotational speed for one revolution of the engine is calculated on the basis of the time period T.sub.i. Thus, an engine combustion variation can be detected by monitoring the sequence of the mean engine rotational speed for every one revolution.
In the prior art method, however, the mean engine rotational speed obtained for one revolution of the engine is affected greatly by the load variation of the engine due to the state of the road on which a vehicle is driven, the transient state of the engine, and the like. Therefore, it is difficult to accurately detect combustion variations.